Answers

Assess/review the technical and economic feasibility of the idea.
Assess/review the sustainability of the startup you are going to create to exploit the idea.
Assess/review the "business plan".
Assess/review the opportunities.
Assess/review the risks.
Assess/review what the competitors are doing.

You can assess/review all such aspects yourself or, even better, you can ask a third party to assess/review them for you... it can certainly help catching the opportunities and handling the risks while following your business plan...

Based on what I have been observing in a number of cases, generally speaking, it really depends on what the startup is doing or proposing to do.

When the required technologies/competences can be easily found in the market, it is highly possible to survive without CTOs and/or co-founders without specific experience/competence. When the new Technologies are being developed as part of the activity of the startup than it is highly recommended to involve people with specific experience/competence (and vision, enthusiasm, capacity to integrate new solutions, etc...), since the earliest stages of development.
In both cases it is highly necessary to invest time and attention in the careful definition of requirements and specifications for the work that (external) development teams will be asked to implement.... this means that if no CTO at least someone with a clear functional view must be present (internally).

In your specific case, I suppose that to be really original creating a "marketplace for freelance developers" you really need to involve asap very skilled and very creative developers who, at same time, have the capacity to specifiy and describe their "dreaming marketplace". whether they need to be co-founders or not is largely a matter of "relationships" and "sharing of risk"...

Reviews

During the time Michele prove to be a very qualified system engineer with specific skills in advanced software for managing coastal marine environment. Marine. His best performances was achieved when he was appointed a Project Manger on European R&D projects with peculiar capabilities in developing very good working and human relationship with the international partners.

I have found Michele to be a very comfortable, knowledgeable and humourous person to work with. We were evaluating technology projects where a broad understanding of complex interactions of teams, different organisations and technologies was required and agreement between us and others was necessary. Michele's skills helped this process.

Michele has been always a great addition to the projects team proposing new strategies and new directions toward customer satisfaction.
Furhtermore he was supporting the technical team with new ideas and suggestions coming from the customers side.
He is also very pleasant to work with and can provide great results if managed appropriately.

Among the positions held by Michele Capobianco with Tecnomare S.p.A., he covered the role of System Engineer/Project Manager/Technologist within the System Engineering Department. Fields of involvement of the Department were oil & gas development projects, environmental monitoring systems and subsea and space robotics. Activities were performed within international co-operation initiatives and hi-tech projects.
q Capacities and technical abilities are: system engineering and project management skill, capability of managing engineering studies both from the technical point of view and with respect to managing relations with client and stakeholders.

The results achieved by Michele were very positive. He tried always to adopt a logical based approach to understanding challenges and work with challenge owners to help deliver results.
He consistently demonstrated a professional and proactive approach in pursuing activities within the team. This was beneficial to the working activities of the department and was appreciated by the other members of the team who sought his advise and support in helping their activities.

"Michele has a deep technical knowledge and he is able to apply this to the management job inside the Company supplying a good management capability with respect to the strategic issues of the company in line with the balance sheet achievements also."